1. Field of the Invention
This invention relates to improved bituminous emulsions, specifically bituminous emulsions of improved viscosity. The invention relates to a method of adding certain nitrogen containing compounds to the bitumen before emulsification with anionic or cationic emulsifiers to provide emulsions of improved viscosity. The nitrogen containing compounds are reaction products of a greater molar amount of tall oil fally acids, rosin, tall oil pitch, petroleum derived acids or esters, vegetable oils, animal oils, tallow fatty acids or any distillation residue which contains carboxylic acid groups reacted with a lesser molar amount of ammonia or amines (to form amides), polyalkylene amines (to form polyamides or imidazoline amides), alkanolamines (to form acid esters), or trialkanolamines (to form aminoesters).
2. Description of the Prior Art
In road construction two major technolgies are now applied to build or repair asphalt wearing courses. One option is to mix fluidized asphalt with dry aggregate and distribute the coated stones evenly on the roadbase or the old surface to be repaired. Smoothing out and compaction is done by rolling the mixes with a pneumatic roller. The other option is to use asphalt in water emulsions. There are several methods of application of emulsifiers which are distinguished by set time or the time it takes for the evaporation of the water at ambient conditions and by the type of the emulsifier used for its production.
Properties of an asphalt emulsion depend greatly upon the chemical used as the emulsifier. That chemical is a surface-active agent, commonly called surfactant, that determines whether the emulsion will be classified as anionic, cationic, or nonionic. The emulsifier also keeps the asphalt droplets in stable suspension and permits breaking at the proper time. The surfactant changes the surface tension at the interface, i.e., the area of contact between the asphalt droplets and the water.
Several chemical emulsifiers are commercially available. The most often used anionic emulsifiers are fatty acids, which are wood-product derivatives such as tall oils, rosins, and lignins. Anionic emulsifiers are saponified (turned into soap) by reacting with sodium hydroxide or potassium hydroxide. Of course, in order to emulsify the oil-based bitumen in water, the emulsifier must be water-soluble.
Most cationic emulsifiers are fatty amines (diamines, imidazolines, amidoamines, to name three). The amines are converted into water-soluble soap by reacting with acid, usually hydrochloric. Another type of emulsifying agent, fatty quaternary ammonium salts, is used to produce cationic emulsions. They are water-soluble salts as produced and do not require the addition of acid to make them water-soluble. They are stable, effective cationic (positively charged) emulsifiers.
Emulsifiers for bituminous emulsions are disclosed in U.S. Pat. Nos. 4,478,642 and 4,494,992 to Schilling et al. These modified reaction products of polyamines with certain polycarboxylic acids and sulfonated carboxylic acids are formed by reacting a greater molar amount of polyamine to a lesser molar amount of the fatty acid and subsequently modifying the reaction product with a variety of reagents taught by the patentees. Also, Schilling, in U.S. Pat. No. 4,547,224, teaches the reaction products of a greater molar amount of polyamines and a lesser molar amount of certain polycarboxylic acid anhydrides as emulsifiers for bituminous emulsions. All of these known emulsifiers, naturally, are water-soluble and exhibit relatively high amine values due to the high content of amine groups in the condensate.
The pH value of the asphalt emulsion is unrelated to its identification as cationic or anionic. Acidity or alkalinity does not determine the sign of the charge. This sign is determined only by the type of emulsifier.
Each emulsifier manufacturer has his own procedure for using his agent in asphalt emulsion production. In most cases, the emulsifier is combined with water before introduction into the colloid mill. In other cases, however, it may be combined with the asphalt cement just before it goes into the colloid mill.
Asphalt is the basic ingredient of the emulsion and, in most cases, it makes up from 55 to 70 percent. The asphalt content is specified for various types of emulsions in ASTM D977 and D2397 which specifications are incorporated by reference herein.
There is not an exact correlation, however, between the properties and the case with which the asphalt can be emulsified. Although hardness of base asphalt cements may be varied as desired, most emulsions are made with asphalts in the 50-250 penetration range. Compatibility of the emulsifying agent with the asphalt cement is essential for production of a stable emulsion.
Asphalt is a colloid composed of several fractions, the major ones being asphaltenes and maltenes. The colloidal make-up of the asphalt depends on the chemical nature and percentage of these fractions and their relationship to each other.
The asphaltenes are the dispersed phase in the alphalt whereas the maltenes are the continuous phase. The asphaltenes are thought to furnish hardness while the maltenes are believed to provide the adhesive and ductile properties of the asphalt. The maltenes present have an influence on the viscosity, or flow properties of the asphalt. The complex interaction of the different fractions make it almost impossible to predict accurately the behavior of an asphalt to be emulsified. For this reason, constant quality control is maintained on emulsion production to detect and correct any tendency of the asphalt to affect adversely the performance of the resulting emulsion.
In the general method of emulsifying asphalts, concurrent streams of molten asphalt cement and treated water are directed by positive displacement pumps into the intake of the colloid mill. The asphalt and emulsifying water are subjected to intense shear stresses as they pass through the colloid mill. The newly formed emulsion may then be pumped through a heat exchanger. The excess heat is used to raise the temperature of incoming emulsifying water just before it reaches the colloid mill. From the heat exchanger, the emulsion is pumped into bulk storage tanks. These tanks sometimes are quipped with some type of stirring device to keep the product uniformly blended.
Heated asphalt cement, the base of the asphalt emulsion, is fed into the colloid mill where it is divided into tiny droplets. At the same time, water containing the emulsifying agent is fed into the colloid mill. The asphalt, as it enters the colloid mill, is heated to ensure a low viscosity, and the water temperature is adjusted accordingly.
As mentioned, asphalt emulsions are divided into three categories: anionic, cationic, and nonionic. In practice, the first two types are ordinarily used in roadway construction and maintenance. Nonionics, however, may be more widely used as emulsion technology advances. The anionic and cationic classes refer to the electrical charges surrounding the asphalt particles. This identification system stems from one of the basic laws of electricity--like charges repel one another and unlike charges attract. When two poles (an anode and a cathode) are immersed in a liquid and an electric current is passed through, the anode becomes positively charged and the cathode becomes negatively charged. If a current is passed through an emulsion containing negatively charged particles of asphalt, they will migrate to the anode. Hence, the emulsion is referred to as anionic. Conversely, positively charged asphalt particles will move to the cathode and the emulsion is known as cationic. With nonionic emulsions, the asphalt particles are neutral and, therefore, do not migrate to either pole.
Emulsions are further classified on the basis of how quickly the asphalt will coalesce; i.e., revert to asphalt cement. The terms RS, MS, and SS have been adopted to simplify and standardized this classification. They are relative terms only and mean rapid-setting, medium-setting and slow-setting. The tendency to coalesce is closely related to the mixing of an emulsion. An RS emulsion has little or no ability to mix with an aggregate, an MS emulsion is expected to mix with coarse but not fine aggregate, and an SS emulsion is designed to mix with fine aggregate.
The emulsions are further subdivided by a series of numbers related to viscosity of the emulsions and hardness of the base asphalt cements. The letter "C" in front of the emulsion type denotes cationic. The absence of the "C" denotes anionic or nonionic. For example, RS-1 is anionic or nonionic and CRS-1 is cationic.
Three grades of high-float, medium-setting anionic emulsions, designated HFMS, have been added to standard ASTM specifications. These grades are used primarily in cold and hot plant mixes, coarse aggregate seal coats, and road mixes. High float emulsions have a specific quality that permits a thicker film coating without danger of runoff.
A quick-set type of emulsion (QS) has been developed for slurry seals. Its use is rapidly increasing as the unique quick-setting property solves one of the major problems associated with the use of slurry seals.
The physical properties of the asphalt emulsions are specified by AASHTO and ASTM (D977 and D2397), which references are incorporated by reference herein. One of the main specifications of the emulsion grades set forth in Table I is minimum and maximum viscosity and the minimum asphalt content.
TABLE I ______________________________________ Cationic Emulsified Emulsified Asphalt Asphalt ______________________________________ RS-1 CRS-1 RS-2 CRS-2 MS-1 -- MS-2 CMS-2 MS-2h CMS-2h HFMS-1 -- HFMS-2 -- HFMS-2h -- SS-1 CSS-1 SS-1h CSS-1h ______________________________________
The "h" that follows certain grades simply means that a harder base asphalt is used. The "HF" preceding some of the MS grades indicates high-float, as measured by the Float Test (AASHTO T 50 or ASTM D 139). High-float emulsions have a quality, imparted by the addition of certain chemicals, that permits a thicker asphalt film on the aggregate particles with minimum probability of drainage. Some user agencies specify an additional cationic sandmixing grade designated CMS-2s, which contains more solvent than other cationic grades.
Asphalt emulsion viscosities are primarily dependent on the amount of asphalt in the emulsion. Other factors include the dosage and type of the asphalt emulsifiers, the pH values of the emulsion, the particle size of the emulsified droplets, the manufacturing condition (temperature, shear, and pressure), the type of colloid mill, the addition of chemical modifiers, the chemical properties of the various components, and the hardness of the base asphalt cement.
The properties of the asphalt cement are very much dependent on the source of the crude oil, the mode of refinement of the crude oil, which bottom product is the asphalt or bitumen, and the type of post-treatment of the bottoms to produce paving grade asphalt.
In recent years, the quality of the asphalt material has changed and in order to meet the viscosity specifications, the emulsifier producers are forced to use either higher amounts of asphalt or an increased concentration of emulsifier. Increased amounts of emulsifier, however, changes demulsibility and set time which is not desired.
For many years, the emulsifier manufacturers and asphalt producers have been exploring ways to change the properties of the asphalt effectively in order to meet viscosity specification at the lowest specified amount of asphalt. Heretofore, no additive to the asphalt has been reported to alleviate this problem.